A clutch assembly of a motor vehicle transmits drive power to a wheel of an axle, and may include a clutch-controlled equalisation unit, having a clutch device. The equalization unit can be engaged and disengaged and can transmit drive power from a first drive member to a second drive member, where the first drive member is on a drive side of the clutch device, and the second drive member is on the output side of the clutch device. An oil-delivering device is provided to oil the clutch, and the oiling of components on the output side of the clutch is provided. The oil-delivering device is arranged on the drive side of the clutch and delivers oil of an oil circuit serving the clutch device, or is immobilised, depending on an operating state.
A clutch assembly of this type is known from DE 10 2008 002 844 A1. In a differential-free, clutch-controlled equalisation unit, a clutch assembly is provided with an activatable multiple disc clutch for a side shaft, which forms the shaft on the output side of the clutch device. Via the multiple disc clutch the drive power is directed to the connected drive wheel of a motor vehicle as required. The outer disc carrier of the multiple disc clutch, which is coupled to the drive-side shaft, delivers lubricating and cooling oil into an oil delivery pocket provided in a housing 16 of the clutch assembly, from which the oil flows back into a sump formed by the housing 16, is picked up again by the clutch, and is fed back to the circuit. An inner oil circuit therefore forms of a disc pack of a side shaft clutch.
Because of this inner oil circuit, a large proportion of the oil volume used for cooling and lubrication remains for a long time in the described inner oil circuit without the oil volume being sufficiently mixed with, or replaced with, “fresh” oil. The oil volume that has only just absorbed heat between the clutch discs is fed directly back to the discs. The clutch temperature therefore increases over-proportionately to the cooling effect that would be achievable with the oil quantity present in the equalisation unit. The over-proportionate heating of the clutches is disadvantageous in terms of the wear behaviour and thus the service life, as well as in terms of the response and control behaviour.
A further disadvantage of the configuration disclosed in DE 10 2008 002 844 A1 is that the clutch packs of the side shaft clutches are in the oil continuously in order to pick it up and deliver it to the oil collection pocket. The associated splash losses increase the power loss of the drive train.
With regard to the undesirable power loss, it is also the case, even in the case described in DE 10 2008 002 844 A1, in which the secondary part of the drive train is decoupled from the drive wheels and the side shaft clutches are completely open, that the secondary drive wheels roll on the road in driving mode and drag the inner disc carrier and the inner discs connected in a rotationally fixed manner thereto. The inner discs, however, are in constant contact with the oil, because they dip therein. Not only is the region of the extremely narrow air gap (gap width approximately 0.1 mm) between the inner and outer discs, which is situated directly in the oil, filled with oil, but the oil is also conveyed into an interspace, not in the oil, between the inner and outer discs of the multiple disc clutch by the rotating inner discs. The liquid friction or hydrodynamic friction produced as a result in turn transmits the drag torque acting on the inner discs from the secondary drive wheels to the outer discs, thereby driving the outer discs. However, as soon as the outer discs begin to rotate, they in turn convey oil into the above-described inner oil circuit and thus increase the oil volume conveyed, and again therefore increase the friction and power loss. The undesirable effect intensifies by itself to a certain extent.
Experiments have shown that because of this effect the secondary drive train is not immobilised even when decoupled from the primary part of the drive train, in contrast to the assumptions made in DE 10 2008 002 844 A1. The negative consequences of this effect can be reduced only slightly by the low-friction design of the surfaces of the inner discs proposed in DE 10 2008 002 844 A1. Moreover, low-friction surfaces of the inner discs result in a much poorer response and control behaviour of the clutch pack. This disadvantage outweighs the power loss advantages that can be achieved with this measure.
A further disadvantage of the clutch assembly disclosed in DE 10 2008 002 844 A1 is that the cooling and lubricating oil must pass through the inner disc carrier or another drive member on the output side of the clutch device. This makes said another drive member complicated to design.
Given this background, a clutch assembly of the type mentioned in the introduction above, having a simplified design, and avoiding the above-described disadvantages is needed. In particular, it would be desirable to optimise the oiling concept described in DE 10 2008 002 844 A1 with regard to the power loss when a secondary part of the drive train is decoupled from a primary part of the drive train without compromising on response and control behaviour of the clutch packs, and without having a negative effect on the functionality of other components. It would further be desirable to ensure that the secondary axle drive train is completely immobilised when it is disconnected, and that components on the output side of the clutch device continue to be supplied with oil despite the oil-delivering device being in the non-delivering state.